Transcription of muscle-specific actin genes in early Xenopus development: nuclear transplantation and cell dissociation.

Cloned cDNA probes that recognize muscle-specific alpha-actin gene transcripts have been used to analyze two kinds of experimental embryos in Xenopus. In one, genetically marked nuclei of larval muscle cells were transplanted to wild-type enucleated eggs; alpha-actin genes became transcriptionally inactive in the resulting blastulae but were reactivated when these embryos reached the normal stage of alpha-actin expression (late gastrula). In the other, blastula embryos reared from fertilized eggs were separated into animal, vegetal, and equatorial regions, and their cells dissociated and reaggregated. alpha-Actin RNA was synthesized at the normal time in development, but only by equatorial cells. We conclude that alpha-actin gene transcription is normally regulated in nuclear-transplant embryos and is undisturbed by the absence of cell contacts during cleavage.